In conventional electrolytic synthesis methods in which fluorine compounds e.g. fluorine, nitrogen trifluoride etc. are produced by electrolysis of hydrogen fluoride in electrolytic baths of hydrogen fluoride-containing molten salts, electrodes of carbon materials are mainly used as anodes. It is however known that, in the case of using such a carbon material electrode in the electrolytic synthesis of the fluorine compound, an insulating layer of graphite fluoride e.g. (CF)n grows on a surface of the carbon material. When the graphite fluoride layer grows to a large thickness on the surface of the carbon material, the area of contact of the electrode with an electrolytic solution in the electrolytic bath becomes reduced to cause a problem of decrease in current flow (which is so called “anode effect”). There is thus adopted a coating technique to apply a coating layer of conducting diamond, on which the growth of a graphite fluoride layer is unlikely to occur, to a carbon substrate surface of the electrode.
In the conventional coating technique, however, it has been practically difficult to completely cover the carbon substrate surface by the conducting diamond coating layer with no minute defects because the conducting diamond coating applied to the carbon substrate is in polycrystalline form. The diamond coating layer undergoes separation when the carbon substrate wears out due to the entry of the electrolytic solution through minute defects in the diamond coating layer.
As a solution to improve this problem, Patent Document 1 discloses a technique for self stabilization of the electrode by forming a graphite fluoride layer on an exposed part of the electrode substrate to which the diamond coating layer is not applied.